Light emitting element and light emitting device using the same

Abstract

An object of the present invention is to provide a light emitting element having slight increase in driving voltage with accumulation of light emitting time. Another object of the invention is to provide a light emitting element having slight increase in resistance value with increase in film thickness. A light emitting element of the invention includes a first layer for generating holes, a second layer for generating electrons and a third layer comprising a light emitting substance between first and second electrodes. The first and third layers are in contact with the first and second electrodes, respectively. The second and third layers are connected to each other so as to inject electrons generated in the second layer into the third layer when applying the voltage to the light emitting element such that a potential of the second electrode is higher than that of the first electrode.

1. A light emitting device comprising:
 a cathode; 
 a first layer over and in direct contact with the cathode, the first layer comprising a first substance with a hole transporting property and a second substance with an electron accepting property with respect to the first substance; 
 a second layer over and in direct contact with the first layer, the second layer comprising a third substance with an electron transporting property and a fourth substance with an electron donating property with respect to the third substance; 
 a third layer over the second layer, the third layer comprising a light emitting substance; and 
 an anode over the third layer. 
 
     
     
       2. The light emitting device according to  claim 1 ,
 wherein the hole transporting property of the first substance is stronger than an electron transporting property thereof, and 
 wherein the electron transporting property of the third substance is stronger than a hole transporting property thereof. 
 
     
     
       3. The light emitting device according to  claim 1 , wherein the cathode is capable of transmitting visible light. 
     
     
       4. An electronic appliance comprising the light emitting device according to  claim 1 . 
     
     
       5. A lighting appliance comprising the light emitting device according to  claim 1 . 
     
     
       6. A light emitting device comprising:
 a cathode; 
 a first layer over and in direct contact with the cathode, the first layer comprising a first substance with a hole transporting property and a second substance with an electron accepting property with respect to the first substance; 
 a second layer over the first layer, the second layer comprising a third substance with an electron transporting property and a fourth substance with an electron donating property with respect to the third substance; 
 a third layer over the second layer, the third layer comprising a light emitting substance; 
 a hole injection layer over the third layer; and 
 an anode over the hole injection layer. 
 
     
     
       7. The light emitting device according to  claim 6 , wherein the hole injection layer comprises an oxide of a metal selected from molybdenum, vanadium ruthenium, tungsten, and manganese. 
     
     
       8. The light emitting device according to  claim 6 ,
 wherein the hole injection layer comprises the first substance and the second substance. 
 
     
     
       9. The light emitting device according to  claim 6 ,
 wherein the hole injection layer comprises a fifth substance with a hole transporting property and a sixth substance with an electron accepting property with respect to the fifth substance. 
 
     
     
       10. The light emitting device according to  claim 9 ,
 wherein the hole transporting property of the fifth substance is stronger than an electron transporting property thereof. 
 
     
     
       11. The light emitting device according to  claim 6 , wherein the hole injection layer is in contact with the anode.